1. Field of the Disclosure
The present invention relates to method for the determination of phenoxy herbicides, e.g., 4-chloro-2-methylphenoxy acetic acid and 4-chloro-2-methylphenoxy propionic acid, in water. The method utilizes a phase transfer catalyst-assisted micro extraction with simultaneous derivatization.
2. Description of Related Art
Following the first reported synthesis of phenoxyherbicides (PHs) in the 1940s, many different types of PHs can now be found. For example, 2,4-dichlorophenoxyacetic (2,4-D), one of the most studied of the PHs, falls within the sub-type, phenoxyacetic acids (Tuxen, N., Reitzel, L. A., Albrechtsen, H.-J., Bjerg, P. L., Ground Water, 2006, 44 256-265-incorporated by reference in its entirety). Other sub-types include phenoxybutyric acids and phenoxypropionic acids. Recently, the syntheses of two new acetate types, 2-chlorophenoxyacetate (2CPA) and 2,4,5-trichlorophenoxyacetate (TCPA), were accomplished (Sarijo, S. H., Bin Hussein, M Z., Yahaya, A. H. J., Zainal, Z., Yarmo, M. A, Current Nanoscience, 2010, 6, 199-205—incorporated by reference in its entirety). Due to the widespread use of PHs, traces of the compounds can now be found in various environmental matrices, such as rivers and drinking water, municipal landfills, in coral Galaxeafascicularis, and in the atmosphere (Marchese, S., Perret, D., Gentili, A., D'Ascenzo, G., Faberi, A., Rapid Commun. Mass Spectrom, 2002, 16, 134-141; Gintautas, P. A., Daniel, S. R., Macalady, D. L., Environ. Sci. Technol, 1992, 26, 517-521; Sabdono, A., Radjasa, O. K., Kang, S., Hur, H.-G., Grossart, H.-P., Simon, M., Zocchi, E., Risk, M. J., Res. J. Env. Toxicol, 2007, 1, 71-77; Waite, D. T., Bailey, P., Sproull, J. F., Quiring, D. V., Chau, D. F., Bailey, J., Cessna, A. J., Chemosphere, 2005, 58, 693-703—incorporated by reference in its entirety).
Following this concern, toxicity studies carried out on different types of PHs indicate a non-specific mode of action through the sub-mitochondrial particle assay with EC50 values ranging between 21 μM and 110 μM (Argese, E., Bettiol, C., Marchetto, D., De Vettori, S., Zambon, A., Miana, P., Ghetti, P. F., Toxicol. in Vitro, 2005, 19, 1035-1043—incorporated by reference in its entirety). The LD50 for male rats is 370 mg kg-1 body weight for 2,4-dichlorophenoxyacetic acid and 700 mg kg-1 body weight for 4-chloro-2-methyl phenoxyacetic acid (CMPA), indicating a slight toxicity (Grabinska-Sota, E., Wisniowska, E., Kalka, J., Crop Protection, 2003, 22, 355-360—incorporated by reference in its entirety). Data on the carcinogenicity, genotoxicity, and mutagenicity of PHs are inconsistent. However, long-term exposure of PHs indicate a strong association of cancer exposure. This toxicity may be explained by free radical formation in humans (Bukowska, B., Rychlik, B., Krokosz, A., Michalowicz, J., Food Chem. Toxicol, 2008, 46, 359-367—incorporated by reference in its entirety). Trace level of PHs detected in the water supplies may represent a potential danger to the living organisms such as plants, animals and possibly humans (Michalowicz, J., Polish J. Environ. Studies, 2005, 14, 327-333; Sterling, T. D., Arundel, A. V., Scand. J. Work Environ. Health, 1986, 12, 161-173—incorporated by reference in its entirety). Thus, it has become especially important to evaluate PHs-contaminated water at trace level.
For quantitative determination of PHs, different extraction and preconcentration methods have been applied for various matrices. Three dimensional liquid microextraction, liquid-liquid-liquid microextraction, was used for bovine milk samples (Zhu, L., Ee, K. H., Zhao, L., Lee, H. K., J. Chromatogr. A, 2002, 963, 335-343—incorporated by reference in its entirety). For the extraction and preconcentration of 2,4-dichlorophenoxyacetic acid, two types of extraction solvents, methanol/acetic acid (99:1) and propanone/water/acetic acid (80:19:1) were used for high humic matter soils that were agitated overnight (Merini, L. J., Cuadrado, V., Giulietti, A. M., Chemosphere, 2008, 71, 2168-2172—incorporated by reference in its entirety). As an example of good PHs recoveries with minimal retention on the sorbent, the use of a dynamic ion-exchange solid-phase extraction (DIE-SPE) was employed (Li N., Lee H. K., Anal. Chem., 2000, 72, 3077-3084—incorporated by reference in its entirety). Furthermore, the efficiency of (DIE-SPE) was highly dependent upon using the correct sorbent. Activated carbon prepared from coals and coconut shells have recently shown great potentials as sorbents for the extraction of PHs from aqueous solutions (Ignatowicz, K., J. Hazard. Mater, 2009, 169, 953-957—incorporated by reference in its entirety). On the other hand, 2,4-dichlorophenoxyacetic acid was more amenable for sorption than other compounds tested because of its limited solubility. As an alternative to using liquid extraction and as an effort to minimize the solvent volume consumed, solid phase microextraction (SPME) could be performed; however, an automated on-line in-tube SPME was performed, and yet, only a dismal extraction recovery (23.9-30.0%) resulted (Takino, M., Daishima, S., Nakahara, T., Analyst, 2001, 126, 602-608—incorporated by reference in its entirety). The recovery via SPME was determined by electrospray ionization mass-spectrometry (ESI-MS) following separation of the analytes through a liquid chromatography column.
Other means of quantitative determination of these compounds include HPLC/diode array detector (DAD), GC-MS, and capillary electrophoresis with ultraviolet detection (CE-UV) (Crespin, M. A., Gallego, M., Valcarcel, M., Gonzalez, J. S., Environ. Sci. Technol, 2001, 35, 4265-4270; Kumar, A., Malik, A. K., Pico, Y., Electrophoresis, 2010, 31, 2115-2125—incorporated by reference in its entirety). The determination of polar and ionizable analytes using GC-MS is problematic due to the difficulty in extracting these types of analytes into organic solvents but also as a result of the poor thermal characteristics of polar analytes typically associated with GC. Chemical derivatization is, therefore, better suited to assist in such determinations of PHs. Using two derivatization reagents, pentylfluorobenzyl bromide and benzyl bromide, low-yield aqueous-phase derivatization was obtained in the SPME-GC-MS method, resulting in a higher detection limit (LOD) (1 μg l−1) (Nilsson, T., Baglio, D., Galdo-Migueza, I., Madsen, J. O., Facchetti, S., J. Chromatogr. A, 1998, 826, 211-216—incorporated by reference in its entirety). In contrast, a different SPME-GC-MS method was reported for phenoxy acid derivatives of butyl chloroformate, but it was also met with a high standard deviation of 20-50% (Henriksen, T., Svensmark, B., Lindhardt, B., Juhler, R. K., Chemosphere, 2001, 44, 1531-1539—incorporated by reference in its entirety).